This project focuses on development and characterization of an in vitro model of hepatic tissue by control of cell-cell interactions. The difficulty in sustaining differentiated hepatocyte functions in vitro has negatively impacted progress towards cell-based therapies for liver disease as well as in vitro experimentation (e.g. drug toxicity studies). It is proposed that an integrated 'biomimetic' platform incorporating key hepatic features (differentiated hepatocytes, compartmentalized metabolism, oriented cell-cell interactions, and directional fluid flow) will serve as a better predictive platform than existing models for Xenobiotic metabolism and physiological experimentation. Preliminary data suggest that co-cultivation of hepatocytes with non-parenchymal cells (fibroblasts) results in long-term differentiated functions, though neither the molecular basis for the 'co-culture effect' nor the dynamics of the process are well understood. In the proposed research, we aim to characterize the dynamics of the co-culture response, uncover the mechanisms that underlie the co-culture response, and incorporate the required elements in a microfabricated array of bioreactors that mimics features of the liver in a high-throughput platform. Specific Aim 1 will be to investigate the dynamic role of homotypic hepatocyte/hepatocyte) gap junction communication and heterotypic (hepatocyte/fibroblast) contact on differentiated functions. The investigator has developed a micropatterning tool that enables control of cell-cell interactions. Electroactive micropatterned surfaces will be utilized to dynamically release fibroblasts from co-culture and study the impact on hepatic function. The mechanism of the 'co-culture effect' was investigated previously using gene expression profiling of various fibroblast strains. Preliminary results indicate that cadherins may play a role in heterotypic signaling. Specific Aim 2 will be to investigate the role of cadherins in coculture, in particular T-cadherin, a candidate that was differentially expressed by over 30-fold. Preliminary results indicate that compartmentalized functions of the liver can be recreated in vitro using controlled oxygen gradients. Specific Aim 3 will be to combine oxygen gradients and directional fluid flow with differentiated hepatocytes (as determined in SA1 & 2) into an array of miniaturized bioreactors that can be used as predictive models of the liver. The engineered tissue will be assessed by examining the responses to well-characterized stimuli. This project will lead to an integrated understanding of how cell-cell interactions produce coordinated organ function and will establish a robust predictive model of liver function for pharmaceutical drug development and fundamental hepatic studies.